Modern integrated circuits, especially microcontrollers or similar programmable integrated circuits are used in a variety of applications which require acting on certain input signals.
In many applications a transition on an input pin, an action, leads to an indication to the outside world via an output pin, a reaction. This form of operation is especially predominant on microcontrollers supporting low power modes.
For example, in the automotive industry, such microcontrollers can be used in window control. When a window switch is pressed, a microcontroller wakes up and executes a window control software. Finally, the window control software drives output pins of the microcontroller to drive the window motor to move the window upwards or downwards. Another example is the headlight control in a vehicle. If the headlight switch is pressed or switched on a microcontroller executes a lamp driver software and directly or indirectly turns on the lamps of the headlights. An indirect control of the lamps can include sending a control signal over a bus system, e.g. a SPI bus. As a last example the seat adjustment can be mentioned, where a seat adjustment switch is pressed and a microcontroller executes a seat control software which drives the seat motors via output pins of said microcontroller.
Common to all these examples is that as a reaction to a signal transition on an input pin of the microcontroller said microcontroller starts executing a software which generates an output signal on another pin of the microcontroller.
To reduce the power consumption of the respective microcontrollers in many applications the microcontroller is put into an energy saving power mode when no input signal is detected at least for a specific amount of time. This reduces the power consumption of the microcontroller but makes necessary a wake up operation on the detection of an input signal on an input pin of the microcontroller.
After a wake up of a microcontroller certain monitoring means in the microcontroller can be activated. Such monitoring means can include a watchdog of the microcontroller or the like. It may happen in some cases that the microcontroller enters an operational state after a wake up procedure which allows the microcontroller to service the watchdog. Therefore, in such a system no error will be detected if there is an error in the microcontroller that allows the microcontroller to service the watchdog but prevents the microcontroller from executing the control software.
US 2009/0271548 shows a method which allows monitoring in a microcontroller if an interrupt is serviced in a predetermined period of time. If this is not the case according to US 2009/0271548 it is possible to raise the interrupt priority or to reset the device.